Gearing Down

So, one of the aspects of using silly-powered brushless motors is that you've got to gear them down a huge amount to make them work properly.

We're looking at two options for gearing down our motor

The first being tried and tested - small pulley meets big pulley, all is well. The issue we have here is that gearing it down to a hopefully safer speed requires some rather small V belt pulleys (unless anyone has a source for 40mm PCD ones?) that will need machining. And I'm not sure we can go below a 40mm PCD, which makes gearing a little too close to our 250MPH tip speed limit that I'm comfortable with - with that gearing, it would be 250.09MPH, assuming 100% efficiency.

Alternatively, we could go down the build-your-own-gearbox route, using timing belts to take the motor speed to something reasonable before attaching it to a standardized set of V pulleys. Along the lines of the Team Whyachi gearboxes - although nowhere near the cost!

Which route do other roboteers take? Should we stick with the KISS route and play the efficiency game? (Realistically, we're probably going to be running at 90% efficiency at a maximum, which puts the tip speed at 225MPH)

Ta

Rob
Team ARC
www.arc-robotics.org.uk

For reference I use a B profile V belt. The celeb bots used twin A profile. You won't find those in anything smaller than 100mm dia or thereabouts. I wouldn't bother using anything smaller belt wise as you are likely to burn it up trying to transfer the power. I'd go for the gearbox to bigger V belt route.

Oh and I've seen the bearings you are planning on using for the drum. I'd go for bigger. 25mm bore on a weapon with the energies you are talking about won't last long.

I really should update the blog.... came to the same conclusion that you have, and went back to the drawing board. I'm leaning towards some large taper rollers and a 90mm stub shaft at the moment, but the limiting speed on them is 8600RPM, which is what we're (hopefully) operating at, so not quite sure how it's all gonna work.

Attachment 6378

We have space for a larger V belt - it's an SPA on there at the moment, but we definitely have space. I have the CAD for a 40mm PCD pulley, up to 3 groove

You have to remember that with bearings they are designed to run for many thousands of hours. You need them to run for a max of 30 minutes (10 fights through robot wars at 3 minutes a piece) plus maybe 5 minutes for testing / tech check etc. Getting close to the max rpm wouldn't be a concern for me.

I wasn't aware that SPA pulleys came that small! May have to look at them again myself.

As far as the rpm limits etc I'd drop the guys at robochallenge an email and ask them what their thoughts on it are.

We've sent a few emails to the RoboChallenge guys and the RW technical people, but we're not expecting a response any time soon, with it being Christmas/New Year time. We're working off of a max tip speed of 250MPH.